Image sensor and method for manufacturing the same

ABSTRACT

An image sensor and method of manufacturing the same are provided. According to an embodiment, the image sensor comprises: a circuit including an interconnection on a substrate; a lower electrode on the interconnection; a separated intrinsic layer on the lower electrode; a second conductive type conduction layer on the separated intrinsic layer; and an upper electrode on the second conductive type conduction layer. The separated intrinsic layer can have an inwardly sloping sidewall to focus light incident the photodiode for the unit pixel.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit under 35 U.S.C. §119 ofKorean Patent Application No. 10-2007-0026730, filed Mar. 19, 2007,which is hereby incorporated by reference in its entirety.

BACKGROUND

In general, an image sensor is a semiconductor device for converting anoptical image into an electrical signal, and is roughly classified as acharge coupled device (CCD) image sensor or a complementary metal oxidesemiconductor (CMOS) image sensor (CIS).

A CIS includes a photodiode and a metal oxide semiconductor (MOS)transistor in each unit pixel. To operate, the CIS sequentially detectselectrical signals of the respective unit pixels in a switching mode,thereby realizing an image.

The related CIS includes a photodiode region that receives an opticalsignal to convert it into an electrical signal, and a transistor regionthat processes the electrical signal.

This related CIS has a structure in which the photodiode and thetransistor are horizontally disposed.

Although the related CIS overcomes drawbacks of the CCD image sensor,the related CIS still has problems to be solved.

Specifically, according to the related CIS having the horizontalstructure, the photodiode and the transistor are formed horizontallyadjacent to each other on the substrate. Thus, the CIS requires anadditional region for the photodiode on the substrate. Thereby, the CISdecreases a region corresponding to a fill factor, and restricts apossibility to increase resolution thereof.

Further, according to the related CIS having the horizontal structure,it is very difficult to optimize a process of simultaneously forming thephotodiode and the transistor. In other words, the process of formingthe transistor requires a shallow junction for low sheet resistance, butsuch a shallow junction is not suitable for the process of forming thephotodiode.

Usually the related CIS having the horizontal structure additionallyprovides on-chip functions. Thus, a size of the unit pixel should beincreased in order to maintain sensitivity of the CIS, or an area forthe photodiode should be decreased in order to maintain a pixel size.However, if the pixel size is increased, the resolution of the CIS isdecreased. Furthermore, if the area for the photodiode is decreased, thesensitivity of the CIS is decreased.

BRIEF SUMMARY

Accordingly, embodiments provide an image sensor and a method formanufacturing the same capable of providing a vertical integration oftransistor circuitry and photodiodes.

Certain embodiments provide an image sensor and the method formanufacturing the same capable of improving resolution together withsensitivity.

An image sensor and method for manufacturing the same according toembodiments of the present invention are capable of employing a verticalphotodiode and inhibiting crosstalk between unit pixels.

An image sensor according to an embodiment of the present inventioncomprises: a circuit including an interconnection on a substrate; alower electrode on the interconnection; a separated intrinsic layer onthe lower electrode; a second conductive type conduction layer on theintrinsic layer; and an upper electrode on the second conductive typeconduction layer.

A method for manufacturing an image sensor according to an embodiment ofthe present invention comprises: forming a circuit including aninterconnection on a substrate; forming a lower electrode on theinterconnection; forming separated intrinsic layers on the substrateincluding the lower electrode; forming a second conductive typeconduction layer on the separated intrinsic layers; and forming an upperelectrode on the second conductive type conduction layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an image sensor according to anembodiment of the present invention.

FIGS. 2 to 7 are cross-sectional views of a manufacturing process of animage sensor according to an embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, an image sensor and a method for manufacturing the sameaccording to embodiments of the present invention will be described indetail with reference to the accompanying drawings.

In the description of embodiments, it will be understood that when alayer (or film) is referred to as being ‘on’ another layer or substrate,it can be directly on another layer or substrate, or intervening layersmay also be present. Further, it will be understood that when a layer isreferred to as being ‘under’ another layer, it can be directly underanother layer, or one or more intervening layers may also be present. Inaddition, it will also be understood that when a layer is referred to asbeing ‘between’ two layers, it can be the only layer between the twolayers, or one or more intervening layers may also be present.

FIG. 1 is a cross-sectional view of an image sensor according to anembodiment of the present invention.

Referring to FIG. 1, in an image sensor according to an embodiment ofthe present invention, it should be noted that the photodiodes, whichare formed above the substrate and receive an incident light from theoutside to convert and maintain the light into an electrical form, canbe PIN diodes.

A PIN diode can be provided as a structure where an n-type amorphoussilicon, an intrinsic amorphous silicon, and a p-type amorphous siliconare bonded. The performance of a photodiode is determined depending onthe efficiency of receiving light from the outside and converting itinto an electrical form, and the total charge capacitance. The relatedart photodiode formed in a substrate generates and stores charge at adepletion region generated in a hetero-junction (for example, P-N, N-P,P-N-P, or N-P-N).

However, the PIN diode is advantageous in generating and storing thecharge, since the entire intrinsic amorphous silicon layer formedbetween the p-type silicon layer and the n-type silicon layer becomesthe depletion region.

When a PIN diode is used as the photodiode of embodiments of the presentinvention, the structure of the PIN diode can be the structure of aP-I-N or an N-I-P. In the described embodiments, the PIN diode havingthe P-I-N structure is used by way of an example, and the n-typeamorphous silicon is referred to as the first conductive type conductionlayer 150, the intrinsic amorphous silicon is referred to as theintrinsic layer 170, and the p-type amorphous silicon is referred to asthe second conductive type conduction layer 180. However, embodimentsare not limited thereto.

In other embodiments, a PIM diode can be used. A PIM diode differs froma PIN diode by utilizing a metal layer (“M”) instead of an n-typeconductive layer (“N”). The metal layer can be any metal that is capableof being silicided at a low temperature, such as a temperature of lessthan 300° C. For example, the metal layer can be formed of Cr, Mo, or W.In embodiments adopting the PIM structure, the lower electrode 140 canbe used as the “M” layer of the PIM diode and no n-type conductive layeris provided.

An image sensor according to an embodiment of the present invention caninclude a circuit including an interconnection 120 on a substrate 100; alower electrode 140 on the interconnection 120; a separated intrinsiclayer 170 on the lower electrode 140; a second conductive typeconduction layer 180 on the intrinsic layer 170; and an upper electrode190 on the second conductive type conduction layer 180. Although theFigures show two metal layers on the substrate (in the interlayerdielectric layer 110), embodiments should not be limited thereto.

The intrinsic layer 170 can be used to focus light toward the lowerelectrode of each unit pixel by having a sloping sidewall. For example,the intrinsic layer 170 can focus light incident the photodiode byhaving inwardly sloping sides. According to an embodiment, the slopingsides can provide a separation between adjacent pixels having longerbottom edge spacing than upper edge spacing.

Also, cross-talk can be inhibited by a void 195 formed between thesecond conductive type conduction layer 180 and the upper electrode 190within the separation between separated intrinsic layers 170.Accordingly, the void 195 can be formed between pixel boundaries.

In a further embodiment, a barrier metal 130 can be formed on theinterconnection 120. The barrier metal 130 can be, for example, W,W-nitride, Ti, Ti-nitride, Ta or Ta-nitride.

In embodiments utilizing a P-I-N or N-I-P structure, a first conductivetype conduction layer 150 can be formed between the lower electrode 140and the intrinsic layer 170.

In the image sensor according to embodiments of the present invention,the transistor circuitry and the photodiodes are vertically integrated.Therefore, the image sensor can have a fill factor approaching 100%. Inaddition, embodiments can provide sensitivity higher than that of therelated horizontally structured image sensor for the same pixel size.

Further, in comparison with the related image sensor, the image sensoraccording to embodiments of the present invention can further reduceprocess cost for the same resolution, and realize more complicatedtransistor circuitry in each unit pixel without reduction of thesensitivity.

In an image sensor according to embodiments of the present invention,additional on-chip circuitry can be integrated to increase performanceof the image sensor, and obtain miniaturization of the device as well asreduction of production cost.

Also, an image sensor according to embodiments of the present inventionis capable of employing a vertical photodiode and can inhibit crosstalkby providing isolation between pixels.

Hereinafter, a method for manufacturing an image sensor according to anembodiment of the present invention will be described in detail withreference to the accompanying drawings.

FIGS. 2 to 7 are cross-sectional views for describing a manufacturingprocess of an image sensor according to an embodiment of the presentinvention.

Referring to FIG. 2, a circuit including interconnections 120 formed inan interlayer dielectric layer (ILD) 110 can be formed on a substrate100.

The interconnections 120 can include a metal line and a plug. The plugcan include a first plug 120 a and a second plug 120 b.

In one embodiment, a barrier metal 130 can be formed on theinterconnections 120. The barrier metal 130 can include, for example, W,W-nitride, Ti, Ti-nitride, Ta, or Ta-nitride. In some embodiments, thebarrier metal 130 can be omitted.

Next, a lower electrode 140 can be formed on the interconnection 120.The lower electrode 140 can be formed of a conductive material includingmetal, alloy or silicide. For example, the lower electrode 140 can beformed of Al, Cu or Co.

The lower electrode 140 can be patterned to each pixel. In someembodiments also including a first conductive type conduction layer 150,the lower electrode 140 can be patterned after forming the firstconductive type conduction layer 150 on the material for the lowerelectrode 140.

According to an embodiment, a first conductive type conduction layer 150can be formed on the patterned lower electrode 140. In some embodiments,the first conductive type conduction layer 150 can be omitted.

The first conductive type conduction layer 150 can serve as the “N-type”layer of a PIN diode. In other words, the first conductive typeconduction layer 150 can include, but is not limited to, an N-typeconductive type conductive layer.

The first conductive type conduction layer 150 can be formed of, but isnot limited to, n-doped amorphous silicon. For example, the firstconductive type conduction layer 150 can be formed of amorphous siliconwith Ge, C, N₂, or O₂ added, such as a-Si:H, a-SiGe:H, a-SiC, a-SiN:H,a-SiO:H, or the like.

In an embodiment, the first conductive type conduction layer 150 can beformed by a chemical vapor deposition (CVD) such as plasma enhanced CVD(PECVD). For example, the first conductive type conduction layer 150 canbe formed of amorphous silicon through PECVD by using a mixture gasobtained by mixing PH3 or P2H5 with silane (SiH4) gas.

According to embodiments of the present invention, cross-talk can beinhibited by using a patterned first conductive type conduction layer150.

Next, forming a separated intrinsic layer 170 according to an embodimentis described as follows.

Referring to FIG. 3, an isolating layer pattern 160 can be formedbetween unit pixels on the substrate.

The isolating layer pattern 160 can include a slope on its sidewall inorder to form an intrinsic layer 170 having sloping sidewalls. Thesloping sidewalls of the intrinsic layer 170 can enable improved lightfocusing towards a pixel's lower electrode 140.

For example, the isolating layer pattern 160, which has a longer bottomsurface than upper surface, can make the intrinsic layer 170 formed onthe isolating layer pattern 160 have a slope. Therefore, the intrinsiclayer 170 can focus light incident to the photodiode by having slopingsides that narrow inward for each unit pixel.

Also, the isolating layer pattern 160 can be made of material which hasa high etching selectivity compared to the intrinsic layer 170. Forexample, the isolating layer pattern 160 can be formed of a photoresist.According to such an embodiment, the isolating layer pattern 160 can bemade to have a longer bottom line than an upper line by setting thephoto condition plus (+) defocus during photoresist patterning.

Referring to FIG. 4, an intrinsic layer 170 can be formed on theisolating layer pattern 160. After forming the intrinsic layer 170, aselective etching of the intrinsic layer 170 using a mask pattern (notshown) can be performed to expose the first plug 120 a, which is to beconnected to an upper electrode (see reference 190 of FIG. 1).

In some embodiments, the selective etching of the intrinsic layer 170can be performed after forming the second conductive type conductionlayer 180. In such embodiments, both the second conductive typeconduction layer 180 and the intrinsic layers can be selectively etchedto expose the first plug 120 a.

The intrinsic layer 170 can serve as an “I-type” layer of a PIN diode.In an embodiment, the intrinsic layer 170 can be formed of non-dopedamorphous silicon. The intrinsic layer 170 can be formed by CVD, such asPECVD. For example, the intrinsic layer 170 can be formed of amorphoussilicon using silane (SiH4) gas by PECVD.

Referring to FIG. 5, the intrinsic layer 170 can be planarized to exposethe isolating layer pattern 160 by a chemical mechanical polishing (CMP)process or the like. Upon performing the CMP process to expose theisolating layer pattern 160, the intrinsic layer 170 is separatedbetween the isolating layer patterns 160. In some embodiments, theintrinsic layer 170 can be formed between the isolating layer patterns160, exposing the isolating layer pattern 160 without planarizing theintrinsic layer 170.

Referring to FIG. 6, the isolating layer pattern 160 can be removed tomake a hole 175 separating the intrinsic layer 170 by unit pixel.Accordingly, the separated intrinsic layer 170 can be formed having aslope on its sidewall and separated by as space by removing theinsulating layer pattern 160. In an embodiment where the isolating layerpattern 160 is photoresist, the isolating layer pattern 160 can beremoved by ashing. In some embodiments, the removing process of theisolating layer pattern 160 can be omitted.

Referring to FIG. 7, a second conductive layer 180 can be formed on theseparated intrinsic layers 170. The second conductive layer 180 canserve as a “P-type” layer of a PIN diode. In other words, the secondconductive layer 180 can include, but is not limited to, a P-typeconductive type conductive layer.

The second conductive layer 180 can be formed of, for example, p-typedoped amorphous silicon. In an embodiment, the second conductive layer180 can be formed by CVD, such as PECVD. For example, the secondconductive layer 180 can be formed of p-type doped amorphous siliconthrough PECVD using a mixture of gas obtained by mixing boron withsilane (SiH4) gas.

Next, an upper electrode 190 can be formed on the upper surface of thesecond conductive layer 180. The upper electrode 190 can be electricallyconnected to the exposed first plug 120 a.

During forming the upper electrode 190, a void 195 may be formed betweenthe second conductive type conduction layer 180 and the upper electrode190. The isolation between unit pixels can be improved by the void 195.For example, the void can be formed by forming the upper electrode 190with a material having low step coverage.

According to certain embodiments, the isolation between unit pixels canbe improved by the void 195 formed between pixels boundaries.

The upper electrode 190 can be formed of a transparent electrode havinggood light transmission and conductivity. For example, the upperelectrode 190 can be formed of indium tin oxide (ITO), cadmium tin oxide(CTO), or ZnO₂. A color filter layer and a microlens can additionally beprovided.

In the image sensor according to embodiments of the present invention,the transistor circuitry and the photodiodes are vertically integrated.Therefore, the image sensor enables a fill factor to approach 100%, andfurthermore can provide sensitivity higher than that of the relatedimage sensor for the same pixel size.

Further, in comparison with the related image sensor, the image sensoraccording to embodiments of the present invention can further reduceprocess cost for the same resolution, and realize more complicatedtransistor circuitry in each unit pixel without reduction of thesensitivity.

Also, in the image sensor according to embodiments of the presentinvention, additional on-chip circuitry can be integrated to increaseperformance of the image sensor, and obtain miniaturization of thedevice as well as reduction of production cost.

Also, the image sensor according to embodiments of the present inventionis capable of employing a vertical photodiode and can inhibit crosstalkby providing isolation between pixels.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. A method for manufacturing an image sensor, comprising: forming acircuit including an interconnection on a substrate; forming a lowerelectrode on the interconnection; forming separated intrinsic layers onthe substrate including the lower electrode; forming a second conductivetype conduction layer on the separated intrinsic layers; and forming anupper electrode on the second conductive type conduction layer, whereinforming the separated intrinsic layers comprises: forming an isolatinglayer pattern in regions between unit pixels; forming intrinsic layersbetween the isolating layer pattern; and removing the isolating layerpattern after forming the intrinsic layers.
 2. The method according toclaim 1, wherein the isolating layer pattern comprises a slopingsidewall.
 3. The method according to claim 2, wherein the isolatinglayer pattern comprises a longer bottom surface than upper surface. 4.The method according to claim 1, wherein the isolating layer patterncomprises a photoresist pattern.
 5. The method according to claim 1,wherein forming the intrinsic layers between the isolating layer patterncomprises forming intrinsic layer material between the isolating layerpattern while exposing a top surface of the isolating layer pattern. 6.The method according to claim 1, further comprising forming a barriermetal on the interconnection before forming the lower electrode.
 7. Themethod according to claim 1, further comprising forming a firstconductive type conduction layer on the lower electrode before formingthe separated intrinsic layers.
 8. The method according to claim 1,wherein the forming of the separated intrinsic layers comprisesproviding a sloping sidewall to the separated intrinsic layers.
 9. Amethod for manufacturing an image sensor, comprising: forming a circuitincluding an interconnection on a substrate; forming a lower electrodeon the interconnection; forming separated intrinsic layers on thesubstrate including the lower electrode; forming a second conductivetype conduction layer on the separated intrinsic layers; and forming anupper electrode on the second conductive type conduction layer, whereinforming the separated intrinsic layers comprises: forming an isolatinglayer pattern in regions between unit pixels; and forming intrinsiclayers between the isolating layer pattern, wherein the forming of theintrinsic layers between the isolating layer pattern comprises: formingan intrinsic layer material on and between the isolating layer pattern;and planarizing the intrinsic layer material to expose the isolatinglayer pattern.
 10. A method for manufacturing an image sensor,comprising: forming a circuit including an interconnection on asubstrate; forming a lower electrode on the interconnection; formingseparated intrinsic layers on the substrate including the lowerelectrode; forming a second conductive type conduction layer on theseparated intrinsic layers; forming an upper electrode on the secondconductive type conduction layer; and forming a void between the secondconductive type conduction layer and the upper electrode during theforming of the upper electrode on the second conductive layer.
 11. Themethod according to claim 10, wherein the void is formed between pixelboundaries.